Re: [PATCH 1/2] PCI: also set up legacy files only after sysfs init

[Pali Rohár]

On Thursday 04 February 2021 15:50:19 Bjorn Helgaas wrote:
> [+cc Oliver, Pali, Krzysztof]

Just to note that extending or using sysfs_initialized introduces
another race condition into kernel code which results in PCI fatal
errors. Details are in email discussion which Bjorn already sent.

> s/also/Also/ in subject
> 
> On Thu, Feb 04, 2021 at 05:58:30PM +0100, Daniel Vetter wrote:
> > We are already doing this for all the regular sysfs files on PCI
> > devices, but not yet on the legacy io files on the PCI buses. Thus far
> > now problem, but in the next patch I want to wire up iomem revoke
> > support. That needs the vfs up an running already to make so that
> > iomem_get_mapping() works.
> 
> s/now problem/no problem/
> s/an running/and running/
> s/so that/sure that/ ?
> 
> iomem_get_mapping() doesn't exist; I don't know what that should be.
> 
> > Wire it up exactly like the existing code. Note that
> > pci_remove_legacy_files() doesn't need a check since the one for
> > pci_bus->legacy_io is sufficient.
> 
> I'm not sure exactly what you mean by "the existing code."  I could
> probably figure it out, but it would save time to mention the existing
> function here.
> 
> This looks like another instance where we should really apply Oliver's
> idea of converting these to attribute_groups [1].
> 
> The cover letter mentions options discussed with Greg in [2], but I
> don't think the "sysfs_initialized" hack vs attribute_groups was part
> of that discussion.
> 
> It's not absolutely a show-stopper, but it *is* a shame to extend the
> sysfs_initialized hack if attribute_groups could do this more cleanly
> and help solve more than one issue.
> 
> Bjorn
> 
> [1] https://lore.kernel.org/r/CAOSf1CHss03DBSDO4PmTtMp0tCEu5kScn704ZEwLKGXQzBfqaA@xxxxxxxxxxxxxx
> [2] https://lore.kernel.org/dri-devel/CAKMK7uGrdDrbtj0OyzqQc0CGrQwc2F3tFJU9vLfm2jjufAZ5YQ@xxxxxxxxxxxxxx/
> 
> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
> > Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> > Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > Cc: Jérôme Glisse <jglisse@xxxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxx>
> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: linux-mm@xxxxxxxxx
> > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> > Cc: linux-samsung-soc@xxxxxxxxxxxxxxx
> > Cc: linux-media@xxxxxxxxxxxxxxx
> > Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> > Cc: linux-pci@xxxxxxxxxxxxxxx
> > ---
> >  drivers/pci/pci-sysfs.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> > index fb072f4b3176..0c45b4f7b214 100644
> > --- a/drivers/pci/pci-sysfs.c
> > +++ b/drivers/pci/pci-sysfs.c
> > @@ -927,6 +927,9 @@ void pci_create_legacy_files(struct pci_bus *b)
> >  {
> >  	int error;
> >  
> > +	if (!sysfs_initialized)
> > +		return;
> > +
> >  	b->legacy_io = kcalloc(2, sizeof(struct bin_attribute),
> >  			       GFP_ATOMIC);
> >  	if (!b->legacy_io)
> > @@ -1448,6 +1451,7 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pdev)
> >  static int __init pci_sysfs_init(void)
> >  {
> >  	struct pci_dev *pdev = NULL;
> > +	struct pci_bus *pbus = NULL;
> >  	int retval;
> >  
> >  	sysfs_initialized = 1;
> > @@ -1459,6 +1463,9 @@ static int __init pci_sysfs_init(void)
> >  		}
> >  	}
> >  
> > +	while ((pbus = pci_find_next_bus(pbus)))
> > +		pci_create_legacy_files(pbus);
> > +
> >  	return 0;
> >  }
> >  late_initcall(pci_sysfs_init);
> > -- 
> > 2.30.0
> > 
> > 
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